Charge forming device



Oct. 5, 1948. L. LEE, 2D 7 2,450,833

CHARGE FORMING DEVICE Filed Nov. 16, 1943 S Sheets-Sheet l INVENTOR.

LEE 1? 0a. 51948. L. LEE, 2:. I 2,450,833

CHARGE FORMING DEVICE I a Sheets-sheaf 2 Filed Nov. 16, 1943 FIG.

AIR FLOW (1w HR.)

FIG.

TO INTAKE MANIFOLD 232 INVENTORQ Wm Luz- 11 BY AIR FLOW HR.)

AGENT Oct L. LEE, 2D 2,450,833

CHARGE FORMING DEVICE Filed Nov. 16, 1943 1 s Sheets-Sheet 3 308 i To INTAKE NVENTOR wmwv LEE :11

AGENT FUEL AIR RATIO AIR v F LOW. (*mR) Patented Oct. 5, 1948 CHARGE FORMING DEVICE Leighton Lee, H, Meriden, Conn., assignor, by to Niles-Bement-Pond Company, West Hartford, Conn., a corporation mesne assignments,

of New Jersey Application November 1c. 1943, Serial No. 510,454

20 Claims. 1

The present invention relates to charge forming devices for internal combustion engines and particularly tosuch devices of the type wherein the quantity of fuel supplied to the engine .is controlled in proportion to the quantity of air flowing to the engine.

In such carburetors, it is common to provide means for controlling the fuel flow so that the fuel-to-air ratio varies in accordance with the engine load, which may conveniently be measured by the air flow. The control of the-fuel-to-air ratio as a function of air flow is usually arranged so that a high fuel to air ratio is provided at air flows less than a first predetermined value, a lower fuel to air ratio during an intermediate range of air flows, and a high fuel to air ratio when the air flow'exceeds a second predetermined value. It is also common to provide a manually operable mixture control by which the pilot may select either a rich fuel-to-air ratio or'a lean fuel-to-air -ratio over the entire range of air flowvariation.

It is an object of the present invention to provide improved means for controlling the fuel to air ratio in a fuel supplysystem for an internal combustion engine.

Another object of the present invention is to provide a mixture control system for a fuel supply system of the type described including a manually operable control device for selecting either a rich fuel-to-air ratio or a lean fuel-to-air ratio,

ment for afuel supply system of the type described ln which the mixture is additionally controlled in' accordance with the pressure in the intake manifold of the engine on which the carburetor is used.

- Other objects and advantages of the present inventionwill become apparent from a consideration of the appended specification, claims and drawing, in which Figure 1 is a somewhat diagrammatic illustration of a carburetor for an internal combustion engine embodying certain of the principles of my invention,-

Figure 2 is a graphical illustration of the relationship between fuel-to-air ratio and air flow in the carburetor of Figure 1, 1

Figure 3 is another somewhat diagrammatic illustration of a diflerent embodiment of the principles of my invention, V

Figure 4 is a graphical illustration of the relationship between thefuel-to-air ratio and a flow in the carburetor of Figure 3,

Figure 5 is a cross-sectional view of a. mixture control system embodying the principles of my invention, and v Figure 6 is a graphical illustration of the relationship between the fuel-to-air ratio and air flow in a carburetor using the mixture control of Figure 5.

FIGURE 1 There is shown in Figure 1 aportion ill of the body of a carburetor of a. type used on an aircraft engine.

i4. Air entering the inlet i 3 flows thru a Venturi restriction it, past a throttle l8, and a fuel discharge nozzle 20 to the outlet it.

- to a vent ring 24 interconnecting the impact tubes 22. From the vent ring 24, this portion of the air flows thru a conduit 26, an expansible chamber 28 in a pressure meter generally indicated at 30. a. restriction 32, another expansible chamber 34 in the pressure meter 30, a conduit 36, a chamber 38 and a conduit 40 to the throat of venturis'lfi.

A valve 42 is' positioned by a flexible bellows 1 44 mounted in the chamber 38, and controls-the flow of air from the conduit into the chamber The pressure difierential between the inletv i3 .and the throat of venturi It varies with theveloc ity of the air flowing thru the passage l2, in accordance with the laws of fluid flow. Since air is of variable density, it is necessary to correct the pressure differential thus obtained for variations in the air density in order to secure a force which may be used asa measure of the mass of air flowing thru passage l2. This. correction is made by the bellows 44, which is sealed so that the position of valve 42 varies with the pressure in the air chamber 38. The bellows 44 may be fllled with nitrogen or other suitable temperature responsive fluid so that the position of valve 42 also varies in accordance with the temperature of the air in chamber 38. Since the density of the An air passage i2 extends thru the body portion in from an inlet iii to an outlet air is determined by its temperature and pressure, it may b seen that the position of valve 42 is a function of the density of the air.

The total pressure differential between inlet I8 and the throat of venturi I8 may be considered as divided into two component pressure drops, one of which is the drop across restriction 82, and the other of which is the drop across valve 42. It may be seen that an increase in the density of the air in chamber 38 tends to open the valve 42, thereby decreasing the component pressure drop across valve 42 and increasing the component pressure drop across restriction 82. In this way, the pressure drop across restriction 82 varies not only with the velocity of the air flowing thru passage I2, but also with the density of that air. By suitably contouring the valve 42,

these two effects may be proportioned so that the pressure drop across restriction 82 varies as a function of the mass of air flowing thru the passage I2 per unit of time.

The air entering in'let I3 may be compressed by a supercharger so that its pressure is considerably above atmospheric. If no supercharger is used, the air inlet is usually provided with a scoop to take advantage of the ram effect due to the motion of the aircraft thru the air.

The mixture leaving the outlet I4 of the carburetor may also be compressed by a supercharger before being delivered to the engine intake manifold.

The fuel for the internal combustion engine comes from a tank (not shown) and flows thru a pump 45 a conduit 48, a fuel pressure regulator generally indicated at 48, a conduit 58, a fuel metering or mixture control system generally indicated at 82, a conduit 58, past an idle valve I48, thru a conduit 54, a. pressure regulator 88, and a conduit 88 to the fuel discharge nozzle 28. The pump 48 is provided with a pressure relief valve 41, which acts to maintain the pump discharge pressure at a substantially constant value. This relief valve may be, for example, of the type shown in the Storch et al. Patent No. 2,157,089.

The pressure meter 88 includes a pilot valve 88 which is operated in accordance with the mass of air flowing thru the carburetor and which controls a fluid pressure so as to operate a main valve 82 in the fuel regulator 48. The pressure regulator 88 maintains a substantially constant pressure on the downstream side of the mixture control 82. The mixture control 52 includes means for varying the cross-sectional area of the I fuel passages extending thru it so as to vary the quantity of fuel flowing thru it for any given pressure differential across it, which pressure differential is determined by the pressure regulators 48and 86. In other words, the mixture control 82 determines the fuel-to-air ratio for any given mass of air flowing thru the passage I2 per unit of time.

The fuel regulator 48 includes a casing 88 divided into two expansible chambers 82 and 88 by a flexible diaphragm 88. The chambers 82 and 88 are interconnected bya restriction 88. The main fuel valve 82 is attached to the center of diaphragm 88 and controls the flow of fuel from conduit 48 into chamber 88 to as to regulate the pressure in chamber 88, which is connected .to conduit 88. The valve 82 is balanced against inlet pressure and is biased toward open position by a spring 8i. A portion of the fuel entering chamber 88 flows thru restriction 89, chamber 82, a conduit 88, valve 88 of pressure meter 88, and conduit 84 to passage I2. The connection of conduit 84 to pas- 4 sage I2 is shown by way of illustration as one method of disposing of the fuel passed by pilot valve 88. That fuel might alternatively be conducted back to the fuel tank, or otherwise disposed of.

The pressure meter 88 includes a casing 84 divided by three flexible diaphragms 88, 88 and 18 into four expansible chambers 12, 28, 84 and 14. The pilot valve 88 is attached to the central portions of the diaphragms, and is biased toward closed position by a spring I8. The chamber I2 is connected by a conduit 18 to the conduit 84 downstream 'from the mixture control 82.

The pressure regulator 88 includes a casing 82 separated by a flexiblediaphragrn 84 into a pair of expansible chambers 88 and 88. A valve I88 is attached to the central portion of diaphragm 84, and is biased toward closed position by a spring I82. The chamber 88 receives fuel from conduit 54. Valve I88 controls the flow of fuel from chamber 88 into conduit 88 so as to regulate the pressure in chamber 88. The chamber 88 is vented thru a conduit I88 to the conduit 28.

The valve I88 in pressure regulator 88 is opened or closed by the diaphragm 84 as necessary to set the pressure in chamber 88 at a value which balances the pressure in chamber 88 and the force of spring I 82. In this way it is insured that the pressure in chamber 88 is always higher than the pressure in chamber 86 by an amount determined by the force of spring I82. Since the pressure in chamber 88 is approximately that at the inlet I8, it is always at least equal to the pressure downstream from throttle I8. Therefore the pressure in chamber 88 is always greater than I the pressure downstream from valve I88. A substantial pressure drop across valve I88 is thereby maintained to insure movement of the fuel thru it. and to prevent vaporization of the fuel at any 40 point upstream from the valve.

. the pressure in chamber 88 would vary with changes in throttle position, etc. However, such variations would be transmitted thru conduit 18 to chamber 12 of pressure meter 88, thereby causing pressure regulator 48 to produce a parallel and equal variation in the pressure upstream from the mixture control system 82. Therefore, variations in pressure in chamber 88 do not affect the fuel pressure differential or the rate of fuel flow thru the fuel metering system.

Fuel entering the mixture control 82 from conduit 88 first enters a chamber I84. From the chamber I84, the fuel may flow thru a flxed metering restriction I88 and a conduit I 81 or thru a fixed metering restriction I88 and a conduit II8. A conduit II2 including a fixed metering restriction II4 branches oil. from the conduit 8. The conduits I81 and H2 terminate in a cylinder H8, in which a piston valve H8 is movable. I

The piston valve I I8 includes a skirt portion I28 of the same diameter as cylinder II8. When in the position shown, the skirt portion I28 closes the conduit H2. The piston valve II8 also includes a recessed portion I22 of substantially smaller diameter than cylinder 8, and located adjacent the port leading to conduit I81. The recessed portion I22 is apertured at I44 to permit the flow oi fuel therethru. The upper end of piston valve II8 extends into a chamber I24 and has a late ally extending tapered flange I28 which may be oved into engagement with the edge of cylinder II 8 to prevent the flow of fuel thru the mixture control system. The chamber I24 is connected to conduit 54.

The valve H8 is operated by a stem I2I which extends longitudinally thruit and thru a port or metering restriction I28 in the bottom of cylinder II6. A metering valve I30 is slidably mounted on the stem I21, and controls the flow thru port I28. 'A compression spring I32 is retained between piston II8 and valve I30, and biases the valve I30 to closed position.

The conduit terminates in a chamber I34 on the opposite side of port I28 from cylinder I I6.

across the mixture control 52. The first pressure diiferential' is produced across restriction 32, as

previously described, and acts on the diaphragm 68 in a direction to close valve 60. Th chamber I2 is connected thru conduit I8 to the downstream side of the mixture control 52. The chamber I4 is connected thru conduit 80 to chamber 82. The

only force acting upwardly on diaphragm 80 is that diaphragm 90 and valve 62 are stationary, the up- A compression spring I36 is retained between the upper wall of chamber I34 and a sealing diaphragm I38 which is attached to stem I21 and extends to the casing of mixture control 52.

The lower end of stem I2I extends outside the casing of mixture control 52 and cooperates with a cam I40 fixed on a shaft I42, which maybe rotated by any suitable means such'as a manu ally operable lever (not shown).

An idle valve I46 is pivotally attached to a lever I43 connected by a link I44 to an arm I45 mounted on the shaft I41 of the throttle I8.

At very low air flows, such as are encountered under idling conditions, the pressure dliferential set up by the venturi I4 tends to be erratic, and is not a reliable indication of the volume of air entering the engine. Theidle valve I46 controls the fuel fiow directly in accordance with the throttle position at such times. The spring I6 in the pressure meter 30 acts on valve 60 in a closing direction. When the differential pressure acting ondiaphragm 68 is small, as under low air flow conditions, the sprin I6 becomes the predominating force acting on valve 60 ina closing direction. then produced by spring I6 causes an increase in the fuel flow thru the main fuel line, since the closure of valve 60 increases the pressure in chamber I4 of pressure meter 30 and hence in chamber 82 of pressure regulator, 48. Furthermore, the spring 9| of pressure regulator 48 biases valve 62 in an opening or'fuel, fiow increasing direction.

The idle valve is normally wide open when the throttle is beyond the range of positions near its closed position, usually termed the idling range. As the throttle moves into the idling range, thereby decreasing the air flow, the idle valve I46 moves toward closed position. At the same time, the springs 5H and I6 cause operation of valve 62 in an opening direction. The valve 62 is thereby opened sufficiently so that its restrictive effect on the fuel flow is less than that of the idle valve I46. Therefore thefuel flow under idling conditions is controlled primarily by the valve I46 in accordance with the position of the throttle, and not by the pressure meter 30 in accordance with the mass of air entering the engine.

Operation of Figure '1 As previously stated, the pressuremeter 30 cooperates with the pressure regulator 48 to control the pressure differential across the mixture control 52 in accordance with the quantity of air flowing thru the passage I2. In the pressure meter 30, the pilot valve 60 is positioned in accordance with ward and downward forces acting on it are balanced. Therefore, it may be seen that for all steady'positions of valve 62, the pressure in chamber 82 differs from that in chamber 88 by a substantially constant amount which corresponds to the force of spring III. The pressure in chambers 82 and I4 may therefore be used as a measure of the pressure in chamber 88 which is substantially the same as the pressure on the upstream side of the mixture control 52. The pressure in chamber I4 acts thru diaphragm I0 in a direction to open valve 60 and the pressure in chamber I2 acts thru diaphragm 66 in a direction to close valve 60. Since the pressure in chamber I4 is higher than that in chamber I2, it may be seen that the pressure differential between these two chambers is a measure of the pressure differential across the mixture control 52, and that this pressure differential acts on valve 60in an opening direction.

The closing movement'pfvalve 60 52 is substantially constant, it may be seen that the pressure meter 30, acting thru fuel regulator 48 controls the pressure differential across the mixture control 52 inproportion to the mass of air flowing thru passage I2.

In any closed hydraulic conduit, the rate of flow of fluid thru an orifice or restriction, or thru a group of parallel restrictions such as the mixture control system 52, is determined by the crosssectional area of the path open to the flow of fuel thru the restrictions and by the pressure differential across the restriction. In the present carburetor, the pressure differential across the mixture control system 52 is varied in accordance with therate of flow of air thru the carburetor. Therefore, it may be stated that the total cross-sectional area open to the flow of fluid thru the mixture control 52 determines the rate of flow of fuel for a given air flow, and hence determinesthe fuelto-air ratio. When the parts of mixture control 52 are in the positions shown in the drawing, fuel can flow thru the mixture control only thru the passage I0I. The passage H2 is closed by the .skirt portion I20 of piston valve H8, and the port I28 is closed by valve I30. The mixture control the difference between a. first pressure differential which is a measure of the pressure difierential is then said to be in its lean position, as indicated by the legend L applied to cam I40.

Under these conditions, the relationship between the fuel and air ratio and the air flow is that indicated by the curve A in Figure 2. When the air fiow is below a certain value, it is so small as compared to the cross-sectional area of venturi I6 that the pressure differential across restriction 7 32 is not a true measure of the mass of air flowing thru passage I2. At such times. the fuel flow is controlled primarily by the idle valve I46, as previously explained. The idle valve I40 is designed to produce a rich fuel-to-air ratio under idling conditions. This is illustrated by the upwardly extending left end portion of curve A. As the air flow increases, the force developed by the pressure differential across restriction 32 controls the fuel flow, the idle valve I48 being moved to an inactive position. The fuel and air ratio then has the low. substantially constant value illustrated in the intermediate range of air fiows in Figure 2. When the air flow exceeds a value indicated by the point I48 in Figure 2, the pressure differential across the valve I30 becomes sufllcient to overcome spring I32, and the valve I30 moves upwardly, opening the port I28. The fuel flow is then increased out of proportion to the increase in air fiow and the fuel-to-air ratio then follows the rising curve appearing at the right end of characteristic A in Figure 2.

When the cam I40 is moved to the rich position indicated by the legend R" in the drawing, the stem I21 is moved upwardly. The skirt portion I20 of piston valve H8 is then moved to uncover the port opening into the passage H2, and the spring I32 is partially released, thereby reducing the closing force acting on valve I30. The relationship between the fuel and air ratio and air flow then follows the curve B of Figure 2. The opening of passage II2 results in an increased fuel-to-air ratio thruout the range of air flows, while the decrease in tension of spring I32 results in the opening of valve I30 at a lower value of air flow, which may be that indicated by the point I50 in Figure 2. In this way, a better performance characteristic of the engine maybe obtained when the mixture control is in the rich position and a better economy characteristic is obtained when the mixture control is in the lean position.

When the cam I40 is moved to the cut-oil. psltion indicated by the legend "C0" in the drawing, the stem I21 is moved downwardly by spring I36 until the flange I26 closes the end of cylinder I I6. At such times, no fuel can flow thru the mixture control 52. This cut-off control may be used for stopping the engine.

FIGURE 3 Figure 3 illustrates a mixture control unit 200 which may be used in place of the mixture control unit 52 of Figure 1. Those elements in Figure 3 which correspond to equivalent elements in Fig- .ure 1 have been given the same reference characters.

Fuel entering the mixture control 200 from the conduit 60 enters a chamber 202 from which it may flow thru a fixed metering restriction 204 to a chamber 206 connected to the conduit 53. Another metering restriction 208 provides a second outlet for the fuel from chamber 202. The restriction 208 is controlled by valve 2I0 biased to closed position by a spring 2I2, and leads to a chamber 2 connected by a fixed metering restriction 2I3 to chamber 206.

A third outlet for fuel from chamber 202 may be traced thru a fixed metering restriction 2I4, an expansible chamber 2I6, past a metering valve 2| 0, thru an annular passage 220 and a conduit 222 to the chamber 2| I.

The valve 2I8 is of the piston type and moves in a cylinder 224. The upper portion of cylinder 224 is tapered as at 225 so as to from a seat for the piston valve 2I8. A stem 226 is attached to valve 2I8 and extends upwardly therefrom, being attached at its upper end to a flexible diaphragm 228 which forms a wall-of the chamber 2I6. A chamber 230 on the opposite side of diaphragm 228 is connected to the intake manifold of the engine thru a conduit 232. Altho the connection to the intake manifold, as shown, is preferred, the conduit 232 may be connected to any point in the air induction system downstream from the throttle.

A spring 234 is retained between valve 2I8 and a piston 23.6 which is also movable in cylinder 224. The spring 234 biases the valve 213 toward closed position. A stem 238 is attached to the lower side of piston236 and extends thru a sealing diaphragm 240 to the outside of the casing of mixture control 200. The end of stem 230 cooperates with a cam 242 fixed on a shaft 244 Operation of Figure 3 When the cam 242 is in the rich position, as shown in the drawing, the relationship between the fuel-to-air ratio and air fiow is that illustrated by the curve C in Figure 4. The spring 234 is designed so that when piston 236 is in the position shown in the drawing, the force required to open the valve 2 I0 is relatively low.

When the mixture control is in the lean position, so that the end of stem 230 engages the low point of cam 242 adjacent the legend L in the drawing, the spring 234 is compressed so that a greater force is necessary to open valve 2I8. For example, if the manifold absolute pressure is 30 inches of mercury, and the mixture control is in its lean position, the fuel and air ratio follows the curve D of Figure 4. As the manifold pressure increases to higher values, the fuel and air ratio follows the curve D only up to a certain value of air flow which varies with the manifold pressure, and then follows one of a series of generally parallel curves indicated by dotted lines in Figure 4, until finally a value of air flow is reached where the fuel and air ratio is following the characteristic curve C of Figure 4. The particular one of the dotted line curves followed by the fuel to air ratio is determined by the particular manifold pressure existing, as indicated FIGURE 5 There is shown in Figure 5 a modified form of mixture control, generally indicated at 250, which may be used in place of the mixture control 52 of Figure 1 or the mixture control 200 of Figure 3. The mixture control 250 combines certain of the features of each of the other two mixture controls 52 and 200. Fuel enters the mixture control 250 through a conduit 50 and leaves through a conduit 53, which conduits may be the 'same as the correspondingly designated conduits of Figure 1.

The mixture control 250 may be selectively set to either rich, lean or cut-off positions by means of a cam 25: fixed on a shaft 254. The shaft 254 may be manually rotated by any suitable lever arrangement. The cam 252 cooperates with a setting. as indicated by the legend on the card 252. The valve 262 is opened so that the Juel I flow is not cut oif or restricted therebii w a valve stem 256 which extends through a cover 258 into a mixture control casing 266. A valve 262 is fixed on the stem 256 within the casing 266, and cooperates with a cylinder 264 formed in e the casing 266.

ing 266. Above the wall 214,'the stem 25,6 is

provided with a shoulder 216. A spring 218 is held in compression between the shoulder 216 and a valve 266, and tends to hold thevalve 286 against a seat member 282 which is threaded into the open end of the casing 266. The valve 286 and seat 282 together form another variable metering restriction. The valve 286 isattached to a stem 284. which extends upwardly through a transverse wall 286 in the seat member 282, and at its upper end is attached to the central portion of a diaphragm 288, which is clamped at its edges between the seat member 282 and a ring'289 attached to the seat member in any suitable man ner. While the inlet pressure acting on valve 286 is substantially balanced by the same pressure acting upwardly on diaphragm 288 in the construction shown, the construction may be modified to unbalance the valve if required.

The assembly consisting of casing 266, seat member 282 and their related parts is inserted in a reces in a casting 296. A chamber 3l8 formed between the diaphragm 288 and the castmg 296 is connected through a conduit 292 to.

the intake manifold of the engine.

Fuel entering the mixture control 256 through the conduit 56 may flow through any of three paths to the conduit 54. One of these paths may be traced from conduit 56 through a fixed metering restriction 292, a conduit 294, cylinder 264,

past valve 262 into a chamber 296 formed in the casing 266 and thence to conduit 54.

A second of these paths may be traced from conduit 56 through a fixed metering restriction 298, a conduit 366, a conduit 362, a chamber 3l5 formed in the casing 266, past valve 268, cylinder 264, past valve 262, through chamber 296 to conduit 54.

The third of the three paths may be traced from conduit 56, through restriction 298, conduit 366, a fixed metering restriction 366, a chamber 368 formed between diaphragm 288 and the wall 286, apertures M6 in the wall 286, past valve 286, into a chamber 3l2 formed in the casing 266, a conduit 314, cylinder 264, past valve 262 into chamber 266 and thence to conduit 54.

A sealing diaphragm M6 is attached at its center to'the stem 256 and at its edge is clamped between cover 258 and casing 266. The fuel pressure acting on the upper side of diaphragm 3i6 aids in holding stem 256 against the cam 252. 1

Operation of Figure 5 When the parts are in the positions shown in Figure 5, the mixture control 256 is in its lean cientiy low that the valve 266 does not open, and

is flowing. through the first of the three paths previously traced. As the air flow through the carburetor increases, the differential pressure across the mixture control 256 increases. When this pressure differential becomes sufficient to overcome spring 216, the valve 266 is moved away from its seat, thereby opening the second path 2 previously traced for the flow of fuel.

The third path for the flowing fuel, which is controlled by valve 286 is opened not only in accordance with the fuel differential pressure across the mixture control system, but also in accordance with the intake manifold pressure acting on the diaphragm 288. Therefore the. valve 286 may open sooner than the valve 266, depending upon the particular value of intake manifold pressure existing.

If the intake manifold pressure remains sumthe cam 252 is in the position illustrated in the drawing, then the relationship between the fuel to air ratio and the air flow is that illustrated by the solid line curve E in Figure 6. .It will be noted that thi curve is substantially a straight line, from the point 326 where the carburetor leaves the idle range to a value 'of air flow indicated by the point 322. At the latter point, the valve 266 is opened and the fuel-to-air ratio thereafter increases rapidly until it is limited by restriction 298, whereupon the curve E again approaches the horizontal.

When the mixture control is in the rich position, so that the stem 256 engages the low point marked R on the cam 252, then the relationship between fuel and air ratio and air flow follows the solid line curve indicated at F in Figure 6. Under these conditions the stem 256 is low, so that the tension of both springs 216 and 218 is reduced, thereby permitting the valves 266 and 286 to open at lower values of fuel pressure differential. The valve 286 then opens at the point 324 in Figure 6 and is fully opened by the time the point 326 is reached. The valve 266 opens at the point 328.

Under the conditions just described, the force of spring 218 determines the air flow at which point 324 occurs. If the force of spring 218 is sumciently reduced, this ystem could be arranged so that the curve F would not extend below its horizontal portion. Such a modification of spring 218 might require corresponding modifications of cam 252 and. diaphragm 288.

When the mixture control is in the lean position illustrated in the drawing, and the intake manifold pressure is high enough to cause opening of valve 286 at a lower value of pressure differential than that indicated by point 322, then the relationship between fuel-to-air ratio and .air flow follows the solid line curve E until the valve 286 opens, whereupon the relationship follows one of a family of curves shown in dotted lines in Figure 6 and marked withthe letter H.

' The particular one of the curves H selected depends upon the intake manifold pressure. It

will be noted that these dotted line curves carry the fuel and air ratio up to a value corresponding to that of the flat part of the solid line curve F, which corresponds to a fully open position of valve 286. As the air flow continues to increase, the fuel and air ratio then-remain at the same value until the point 336 is reached, whereupon the valve 266 is opened and the fuel-to-air ratio While I have shown and described certain preferred embodiments of my invention, other modifications thereof will readily occurto those skilled in the art and I therefore intend my invention to be limited only by the appended claims.

I claim as my invention:

' l5 1. A fuel supply system for an internal combustion engine including a fuel pump, a fuel conduit extending from said pump to said engine, a first metering restriction in said conduit, means for varying the pressure diflerential across said re-- striction to control the fuel fiow therethru, first valve means for controlling the cross-sectional area of said restriction in accordance with said pressure differential, spring means biasing said first valve means to'closed position and acting inopposition to said pressure difi'erential, a second metering restriction connected in parallel with said first restriction, second valve means for controlling the flow thru said second restriction, second spring means biasing said second valve means to closed position, manually operable means for opening said second valve means against said second spring means, and means operative as an incident to opening of said second valve means to reduce the tension of said first spring means so that said first valve means opens at a lower pressure differential.

2. A fuel supply system for an internal combusion engine comprising a first conduit for air flowing to said engine for combustion purposes;

means associated with said conduit for producing two unequal pressures whose diflerence is a measure of the quantity of air flowing therethru, a fuel pump, a main fuel conduit extending from said pump to said engine, means responsive to said difference of pressures for controlling the fiow of fuel thru said fuel conduit, a plurality of parallel branch fuel conduits, a metering restriction in each of said branch conduits. a cylinder forming a connection between said branch conduits and said main conduit, one of said branch conduits opening into a port in one end of said cylinder, the others of said branch conduits opening into ports in the sides of said cylinder, and said main. conduit opening into the other end of said cylinder, a piston valve movable in said cylinder, said valve being effective upon movement in one direction first to close one of said lateral ports and then to close said other end of said cylinder, a poppet valve for go controlling the port in said one end of cylinder,

compression spring means extending between said poppet valve and said piston valve and biasing said poppet valve to closed position, and means for controlling the ratio of fuel to air supplied to said engine including manually operable means for moving said piston valve so as to control said lateral ports and to change the force of said compression spring means.

3. A fuel supply system for an internal oombus- 7 tion engine comprising means for measuring the quantity of air flowing to said engine for combustion purposes, a fuel conduit, means responsive to said air measuring means to control the quantity of fuel supplied to said engine thru restrictions and subject to a force acting in an opening direction and varying in accordance with said quantity of air, spring means biasing said valve for movement toward closed position, a second valve controlling the fuel fiow thru the other of said restrictions, manually operable means for operating said second valve, and means forming a part of said second valve for varying the force of said spring means.

4. A fuel supply system for an internal combustion engine including a fuel pump, a fuel conduit extending from said pump to said engine, a pair of parallel metering restrictions in said conduit, means for varying the pressure difierential across said restrictions to control the fuel flow therethru, a first and second valve means for coordinately controlling the cross-sectional area ofsaid restrictions in accordance with said pressure differential, a first spring biasing the said first valve means toward closed position; a second spring associated with both of said valve means for biasing the said second valve means toward closed position and the said first valve means toward open position, additional means for applying an opening force to one of said valve means, and means for simultaneously varying the tension of both said spring means.

5. A fuel supply system for an internal combustion engine including a fuel pump, a fuel conduit extending from said pump to said engine, a pair of parallel metering restrictions in said conduit, means for varying the pressure differential across said restrictions to control the fuel fiow therethru, a pair of valves for coordinately controlling the cross-sectional area of said restrictions in accordance with said pressure differential, a spring operatively associated with each of said valves respectively for biasing said valves toward closed position in opposition to said pressure differential, one of said springs also biasing one of said valves toward open position, means responsive to the pressure in the intake manifold of said engine for applying an addi one of said restrictions in accordance with said fuel pressure differential, a second valve for controlling the fiow thru another of said restrictions, spring means biasing said first valve to closed position, a cut-off valve in series with all said parallel restrictions, a stem for said cut-off valve, retainer means for said spring means attached to said stem and eflective to vary the valve closing force of said spring means in accordanc with the position of said stem, cam means for moving said stem, a manual operator for said cam means movable between a first position wherein said cut-off valve is closed, a second position wherein said cut-off valve is open and the force.

means .is set at a second predeterminedvalue, and means", connecting said second valve and said stem and effective to influence said second valve in an opening sense when said operator is moved to its third position.

7. A fuel supply system for an internal combustion engine, including a conduit for fuel flowing toward said engine, a plurality of parallel metering restrictions in said conduit, means for controlling the fuel pressure differential across said restrictions to regulate the fuel flow therethru, a first valve for controlling the fiow thru one of said restrictions in accordance with said fuel pressure differential, spring means biasing said valve to closed position, a cut-off valve in series with all said parallel restrictions, a stem for said cut-off valve, retainer means for said spring means attached to said stem and effective to vary the valve closing force of said spring means in accordance with the position of said stem, cam

means for moving said stem, and a manual operator forsaid cam means movable between a, first position wherein said cut-off valve is closed, a second position wherein said cut-off valve is open and the force of said spring means is set at a first 25 predetermined value, and a third position wherein said cut-off valve is open and the force of said spring means is set at a second, predetermined value. g r

8. A fuel supply system for an internal combustion engine, including a conduit for fuel fiowing toward said engine, a plurality of parallel metering restrictions in said conduit, means for controlling the fuel pressure differential across said restrictions to regulate'the fuel fiow therethru, a first valve for controlling the flow thru a first position wherein the force of said spring means is set at a first predetermined value, and a second position wherein the force of said spring means is set at a second predetermined value lower than said first value, and means connectin said second valve and said positioning means and effective to influence said second valve in an opening sense when said operator is moved to its second position.

9. A fuel supply system for an internal combustion engine, including a conduitfor 'fuel fiowing toward said engine, a plurality of parallel metering restrictions in said conduit, means for controlling the fuel pressure differential across said restrictions to regulate the fuel fiow therethru, a first valve for controlling the fiow thru one of said restrictions in accordance with said fuel pressure differential, springmeans biasins said valve to closed position, a second valve for controlling the flow thru another of said restrictions, means for varying the valve closing force of said spring means, a manual operator for said force varying means movable between a first position wherein the force of said spring means is set at a first predetermined value, and a second posi-' tion wherein the force of said spring is set at a second predetermined value lower than said first value, and means connecting said second valve and said operator and effective to infiuence said second valve in an opening sense when said operator is moved to its second position.

10. A fuel supply system for an internal combustion engine, including a conduit for fuel nowing toward said engine, a plurality of parallel -metering restrictions in said conduit, means for controlling the fuel pressure differential across said restrictions to regulate the fuel fiow therethru, a first valve for controlling the flow thru 19 one of said restrictions in accordance with said fuel pressure differential, spring means biasing said valve toclosed position, a second valve for controllingthe flow thru another of said restrictions, means for varying the valve closing force of 1 said spring means, a manual operator for said force varying means movable between a first position wherein the force of said spring means is set at a first predetermined value, and a second posi-.

tion wherein the force of said spring is set at a 20 second predetermined value lower than said first value, and means rigidly connecting said second valve and said operator and effective to open said second valve when said operator is moved to its second position. r

11. A fuel supply system for an internal combustion engine, including a conduit for fuel fiowing toward said engine, a plurality of parallel metering restrictions in said conduit, means for controlling the fuel pressure differential across said restrictions to regulate the fuel fiow therethru, a first valve for controlling the fiow thru one of said restrictions in accordance with said fuel pressure differential, spring means biasing said valve to closed position. .a second valve for controlling the fiow thru another of said restrictions, means for varyingthe valve closing force force varying means movable between a first position wherein the force of said spring means is set at a first predetermined value, and a second position wherein the force of said spring is set at a second predetermined value lower than said first value, and spring means flexibly connecting said operator and said second valve and effective to influence said second valve in an opening sense when said operator is moved to its second position.

12. A fuel supply system for an internal combustion engine, including a conduit for fuel flow- 0 ing toward saidengine, a plurality of parallel thru, a first valve for controlling the flow thru one of said restrictions, said valve being unbalanced so that said fuel pressure differential tends to open said valve, means including a spring for applying a closing force to said valve in opposition to said fuel pressure differential, a second valve for controlling the flow thru another of said restrictions. means for operating said second valve selectively to open and closed positions, and

means operative as an incident'to operation of said second valve to vary the closing force acting 55 on said first valve, said last-named means being effective when said second valve is opened to decrease the closing force acting on said first valve and effective when said second valveis closed to increase the closing force acting on said first valve.

, 13. A fuel supply system for an internal combustion engine, including a conduit for fuel fiowing toward said engine, a plurality of parallel metering restrictions insaid conduit, means for 7 controlling the fuel pressure differential across of said spring means, a manual operator forsaid 15 said restrictions to regulate the fuel flow therethru, a first valve for controlling the fiow thru one of said restrictions, said valve being unbalanced so that said fuel pressure differential tends to open said valve, means including a spring for applying a closing force to said valve in opposition of said fuel pressure differential, a second valve for controlling the flow thru another of said restrictions, means for operating said second valve selectively to open and closed positions, and means operative as an incident to operation of said second valve to varythe net closing force acting on said first valve, said last-named means being effective when said second valve is opened to establish a first predetermined value of said fuel pressure differential at which said first valve opens and effective when said second valve is closed to establish a second predetermined value of said fuel pressure differential at which said first valve opens, said second value being greater than said first value.

14. Fluid fiow controlling apparatus, comprising a fluid conduit, a plurality of parallel branch conduits connecting spaced portions of said main conduit,.at least one metering restriction in each said branch conduit, a first valve for controlling the flow thru one of said restrictions in accordance with the fluid pressure differential thereacross, a second valve for controlling the fiow t'hru another of said restrictions, spring means biasing said first valve to closed position, a/cutoff valve in series with all said parallel restrictions, a stem for said cut-off valve, retainer means for said spring means attached to said stem and effective to vary the valve closing force of said spring means in accordance with the position of said stem, cam means for moving said stern, a manual operator for moving said cam means between a first position wherein said cut-off valve is closed, a second position wherein said cut-01f valve is open and the force of said spring means 15. Fluid fiow controlling apparatus, comprising a fluid conduit, a plurality of parallel branch conduits connecting spaced portions of said main conduit, at least one metering restriction in each said branch conduit, a first valve for controlling the fiow thru one of said restrictions in accordance with the fluid pressure differential-thereacross, spring means biasing said valve to closed position, a second valve for controlling the fiow thru another of said restrictions; means for varyin the valve closing force of said spring means, a manual operator for said force varying means movable between a first position wherein the force of said spring means is set at a first predetermined value, and a second position wherein the force of said spring means is set at a second predetermined value lower than said first value, and means connecting said valve and said operator and effective to influence said second valve in an opening sense when said operator is moved to its second position.

16. Fluid fiow controlling apparatus, comprising a fiuid conduit, aplurality of parallel branch conduits connecting spaced portions of said main conduit, at least one metering restriction in each said branch conduit, a first valve for controlling the flow thru one of said restrictions, said valve 16 being unbalanced so that the fiuid pressure differential across said restriction tends to open said valve, means including a spring for applying a closing force to said valve in opposition to said fiuid pressure differential, a second valve for controlling the fiow thru another of said restrictions, means for operating said second valve selectively to open and closed positions, and means operative as an incident to operation of said second valve to vary the net closing force acting on said first valve, said last-named means being effective when 'said second valve is opened to establish a first predetermined value of said fluid pressure differential at which said first valve opens and effective when said second valve is closed to establish a second predetermined value of said fiuid pressure differential at which said first valve opens, said second value being greater than said first value. i

17. A fuel supply system for an, internal combustion engine, comprising a first main conduit for conveying combustion air to said engine, a second main conduit for conveying fuel to said engine, first and second parallel branch conduits connected in series with said second main conduit, a mixture control valve located at a Junetion of said parallel branch conduits and said second main conduit, said mixture control valve being movable between a first position wherein only said first parallel branch conduit is open to the fiow of fuel and a second position wherein both of said parallel branch conduits are open to the flow of fuel, first and second fixed metering restrictions in said first and second parallel branch conduits, respectively, means responsive to the rate of flow of air through said first main conduit for regulating the fuel pressure differential across said restrictions to control the rate of flow of fuel therethru, said pressure differential regulating means, said restrictions and said mixture control valve co-oper-ating when said mixture control valve is in said first position to maintain a first predetermined fuel-to-air ratio and when said mixture control valve is in said second position to maintain a second predetermined fuel-to-air ratio greater than said first ratio, a single enrichment valve connected in parallel with said restrictions, said enrichment -valve being acted upon in an opening sense by said fuel pressure differential, spring means biasing said enrichment valve toward closed position, and means effective upon movement of said mixture control valve from said first to said second positions to vary in a valve-opening sense a force acting on said enrichment valve, said enrichment valve and said force varying means cooperating with said pressure differential regulating means to increase the fuel-to-air ratio above said first predetermined value at first fuel pressure diiferential value when said mixture control valve is in said first position and to increase the fuel-to-air ratio above said second predetermined value at a second lower fuel pressure differential value when said mixture control valve is in said second position.

18. Fluid fiow control apparatus, comprising a main conduit, a pair of parallel branch conduits connecting two spaced portions of said main conduit, a selector valve at one of the Junctions of said branch conduits with said main conduit, said selector valve being movable between a first position wherein only one of said branch conduits is open and a second position wherein both of said branch conduits are open, metering restrictions ineach of said branch conduits, said said fluid pressure 'difierential, said difi'erential acting on said single valve in an opening sense, spring means biasing said single valve to closed position, and means effective upon movement of said selector valve from said first to said second positions to vary in a valve-opening sense a force acting on said single valve, 50 that said single valve opens when said selector valve is in said first position at a first predetermined value of said pressure differential and when said se- 18 bustion air flowing to said engine, a. throttle in said conduit, a conduit for fuel flowing to said engine, metering restriction means in said fuel.

conduit, means responsive to the rate of flow of combustion air to said engine for controlling the fuel pressure difierential across said metering restriction means to regulate the flow of fuel therethru, first enrichment valve means responsive to said fuel pressure diiferential for varying the area of said restriction means, first spring means biasing said first enrichment valve means closed and efiective to hold said first valve means closed I until said fuel pressure difierential exceeds a predetermined value, second enrichment valve means responsive to the pressure in sai-d'air'conduit downstream from said throttle for varying the area of said restriction means, and second spring lector valve is in said'second position at a second lower value of said pressure differential.

19. A fuel supply system for an internal combustion engine, comprising a conduit for fuel flowing toward said engine, metering restriction means in said conduit, means for controlling the fuel pressure differential across said metering restriction means to regulate the flow of fuel therethru, enrichment valve means for varying the area of said restriction means, and operating means for said enrichment valve means including a movable wall separating first and second expansible chambers, means for communicating to said first chamber the pressure. in the intake manifold ofsaid engine, means for communicating to said second chamber the fuel pressure on the upstream side of said enrichment valve means, said wall being associated with said valve means so that' movement of said wall accompanying an increase in pressure in said first chamber causes an opening movement of said enrichment valve means.

20. A fuel supply system for an internal combustion engine, comprising a-conduit for commeans biasing said second enrichment valve means closed and effective to hold said second valve means closed until said air conduit pres sure exceeds a predetermined value.

, LEIGHTON LEE, II.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENT FOREIGN PATENTS Country Date Great Britain Sept. '7, 1911 Great Britain Feb. 5, 1925 Great Britain July .25, 1940 Australia May 15, 1941 Number Number 19,977 228,300 

